Wireless communications systems comprising wireless networks, in which a user equipment (UE) such as a mobile handset communicates via wireless links to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations of radio access technology. The initial deployment of systems using analogue modulation has been superseded by second generation (2G) digital systems such as GSM (Global System for Mobile communications), typically using GERA (GSM Enhanced Data rates for GSM Evolution Radio Access) radio access technology, and these systems have themselves been replaced by or augmented by third generation (3G) digital systems such as UMTS (Universal Mobile Telecommunications System), using the UTRA (Universal Terrestrial Radio Access) radio access technology. Third generation standards provide for a greater throughput of data than is provided by second generation systems; this trend is continued with the proposals by the Third Generation Partnership Project (3GPP) of the Long Term Evolution (LTE) system, using E-UTRA (Evolved UTRA) radio access technology, which offers potentially greater capacity and additional features compared with the previous standards.
LTE is designed as a high speed packet switched network, and voice services are provided as packet switched voice services and in particular Voice over Internet Protocol Multimedia Subsystem (VoIMS), whereas previous generation systems such as UMTS support voice services that are primarily circuit switched. Therefore, for LTE, both data and voice services are provided by a packet switched network, and a circuit switched connection is generally not available. The packet switched network is typically “always on”, so that following a successful initial attachment, a user equipment remains connected to a packet data network.
If an initial attachment fails, then the user equipment may have no connectivity to the packet data network. This may occur, for example, if the user equipment requests connection to a packet data network associated with an access point name that is invalid or not available, or if the user equipment requests connection to a packet data network associated with an access point name to which the user equipment is not authorised to connect; a failure of authorisation may occur, for example, due to entering an invalid password.
In circuit switched systems, if a user equipment is denied access to a packet data network, a channel is typically available to allow the user equipment to be contacted with instructions as to how to connect to the packet data network, such as, for example, instructions on how to request a replacement password. For example, an SMS message may be sent to the user equipment.